1. Field of the Invention
Citrate esters are useful as plasticizers for polyvinyl chloride (PVC) resins as certain of these esters provide a low order of toxicity when compared to phthalate esters which have been conventionally used. Other advantages have been noted using certain citrate esters as plasticizers in PVC compositions and articles, including improved resistance to soapy water extraction and low temperature and transport properties.
Medical articles formed from PVC compositions utilizing certain citrate esters as plasticizers provide an improved environment for whole blood and blood platelets compared to PVC formulations utilizing conventional plasticizers. Such medical articles may consist of:
1. bags for the storage of whole blood, packed red cells, platelets and plasma; PA0 2. intravenous tubing for the transportation of blood, blood products and crystalloid intravenous fluids; PA0 3. indwelling intravenous and intra-arterial catheters; and PA0 4. tubing-flexible having contact with whole blood as used in: PA0 R.sub.4 =CH.sub.3 to C.sub.7 H.sub.15
(a) renal dialysis devices; PA1 (b) corpuscular oxygenators as used in open heart surgery; PA1 (c) membrane oxygenators for pulmonary failures; PA1 (d) phagocytosis for the collection of platelets and leucocytes for transfusions; and PA1 (e) intensive plasma exchange devices.
The preparation of the citrate esters has been found to be significantly enhanced by the utilization of certain organic titanate catalysts which allow the excess alcohol to be removed after the esterification step.
2. Description of the Prior Art and Objectives of the Invention
Citrate esters commercially produced using citric acid have long been available and have been used as plasticizers for PVC resins. However, the performance of articles produced from the PVC resin compositions whether utilizing citrate esters known to date or conventional phthalate plasticizers have had many inherent disadvantages. For example, medical-grade PVC compositions are used to form blood bags, tubing and a variety of health-related articles and in recent years toxicity has been a major concern for manufacturers of such articles. Recent reports have identified di-2-ethylhexyl phthalate (DEHP) or (DOP) and di-2-ethyl-hexyl adipate (DEHA) as hepatocarcinogens in rodents.
In vitro studies have demonstrated significant growth inhibition of human diploid fibroblasts at DEHP concentrations that are found in whole blood stored for 21 days and platelets stored for 24 hours in conventional blood bags. Transfusion studies in monkeys revealed physiological and histological liver abnormalties for up to 26 months after the cessation of transfusions. Patients undergoing kidney dialysis received an amount of DEHP approximately 10 to 20 times that which produced liver damage in the monkeys. DEHP has also been demonstrated to be a peroxisome proliferator and probably a hepatic carcinogen in animals. These results were largely supported by the standard National Cancer Institute National Toxicology Bioassay Program Study in rats and mice.
Industry's attempt at developing alternative PVC plasticizers have been met with limited success. Two of the polymers utilized in a recent comparative study, PVC-TOTM and polyolefin are presently approved for the storage of blood platelets for up to seven days. This is based on both in vivo survival and function studies and their improved gas permeability as compared to PVC-DEHP. The above formulations (PVC-DEHP and polyolefins) and all others attempted to date have not proven suitable for red cell survival studies. The formulations mentioned also show an increase in osmotic fragility of red cells, elevated plasma hemoglobin levels, and red cell potassium levels. This would implicate red cell membrane lesions.
While certain of the phthalates have excellent plasticizing qualities, their suspected carcinogenic nature renders them doubtful candidates for future medical-grade uses. As an alternative, known citric acid esters such as acetyltri-n-butyl and tri-n-butyl citrate were tried as PVC plasticizers in medical-grade applications but it was determined that these compounds were not entirely satisfactory due to their high soapy water extraction percentages and would therefore not be useful in many medical area applications. Also, it has been found that new production techniques had to be devised for the newer citric acid esters which were determined to have suitable toxicity and physical characteristics when used as PVC plasticizers.
It is therefore an objective of the present invention to provide PVC plasticizers which provide superior toxicity test results in biological studies.
It is also an objective of the present invention to provide plasticizers for PVC compositions which can be processed without difficulty using conventional extrusion, calendering, or plastisol techniques.
It is yet another objective of the present invention to provide new citric acid esters namely: acetyltri-n-hexyl citrate, n-butyryltri-n-hexyl citrate, acetyltri-n-(hexyl/octyl/decyl) citrate, and acetyltri-n-(octyl/decyl) citrate which can be used as plasticizers having desirable physical characteristics when imparted into PVC compositions.
It is still another objective of the present invention to provide PVC compositions and formed articles therefrom having superior results in toxicology studies concerning dermal toxicity, oral toxicity and genetic assays.
Another objective of the invention is to provide a medical article and process for making the same such as a blood bag which will provide an improved environment for containing whole blood or blood platelets.
It is also an objective of the present invention to provide a new process for the manufacture of the four new citric acid esters utilizing organic titanates to provide economical and efficient production methods.
Others objectives and advantages of the present invention will be demonstrated to those skilled in the art as set forth in detail below.